RF transceiver front-end with RX/TX isolation

Abstract

A radio frequency (RF) transceiver front-end includes an antenna, an RF receiver section, an RF transmitter section, a balancing circuit, and a multiple node isolation and coupling circuit. The multiple node isolation and coupling circuit is coupled to the antenna, the RF receiver section, the RF transmitter section, and the balancing circuit. The multiple node isolation and coupling circuit provides an inbound RF signal from the antenna to the RF receiver section and provides an outbound RF signal from the RF transmitter section to the antenna, wherein, by providing an isolating signal to the balancing circuit, the multiple node isolation and coupling circuit substantially isolates the outbound RF signal from the inbound RF signal.

1. A radio frequency (RF) transceiver front-end comprises:
 an antenna; 
 an RF receiver section coupled to convert an inbound RF signal into an inbound baseband or near baseband signal; 
 an RF transmitter section coupled to convert an outbound baseband or near baseband signal into an outbound RF signal; 
 a balancing circuit; and 
 a multiple node isolation and coupling circuit comprising a transformer balun having a first winding, a second winding, and a third winding, wherein: the second and third windings are serially coupled, wherein the antenna is coupled to a node of the first winding, the RF receiver section is coupled to a first node of the second winding, the RF transmitter section is coupled to a second node of the third winding, and the balancing circuit is coupled to a series connection of the second and third windings and a plurality of capacitors coupled to the first, second, and third windings, 
 wherein the multiple node isolation and coupling circuit provides the inbound RF signal from the antenna to the RF receiver section and provides the outbound RF signal from the RF transmitter section to the antenna, wherein, by providing an isolating signal to the balancing circuit, the multiple node isolation and coupling circuit substantially isolates the outbound RF signal from the inbound RF signal. 
 
     
     
       2. The RF transceiver front-end of  claim 1  further comprises:
 an integrated circuit (IC) the includes the RF receiver section, the RF transmitter section, the balancing circuit, and the multiple node isolation and coupling circuit. 
 
     
     
       3. The RF transceiver front-end of  claim 1 , wherein the RF receiver section and the RF transmitter section have substantially equal impedances within a frequency range and frequencies of the inbound and outbound RF signals are within the frequency range such that the transformer balun is a symmetrical transformer balun. 
     
     
       4. The RF transceiver front-end of  claim 1 , wherein, within a frequency range, impedance of the RF receiver section does not substantially equal impedance of the RF transmitter section and wherein frequencies of the inbound and outbound RF signals are within the frequency range such that the transformer balun is an asymmetrical transformer balun. 
     
     
       5. The RF transceiver front-end of  claim 1 , wherein the multiple node isolation and coupling circuit comprises:
 an autotransformer having a first winding and a second winding coupled in series, wherein a first node of the first winding is coupled to the RF transmitter section and to a first node of the balancing circuit, a second node of the second winding is coupled to the RF receiver section and to a second node of the balancing circuit, a series connection of a second node of the first winding to a first node of the second winding is coupled to the antenna; and 
 a plurality of capacitors coupled to the first and second windings. 
 
     
     
       6. The RF transceiver front-end of  claim 1 , wherein the balancing circuit comprises:
 an adjustable impedance network to provide a desired impedance of the balancing circuit with respect to impedances of the RF receiver section and the RF transmitter section. 
 
     
     
       7. The RF transceiver front-end of  claim 5 , wherein the balancing circuit further comprises:
 an adjustable capacitor network coupled to the adjustable impedance network, wherein the adjustable capacitor network is adjusted to change an isolation frequency center of the multiple node isolation and coupling circuit. 
 
     
     
       8. The RF transceiver front-end of  claim 1 , wherein the RF receiver section and the RF transmitter section are operable to support cellular communications. 
     
     
       9. The RF transceiver front-end of  claim 1 , wherein the RF receiver section and the RF transmitter section are operable to support Wireless Local Area Network communications. 
     
     
       10. An integrated circuit (IC) comprises:
 an RF receiver section coupled to convert an inbound RF signal into an inbound baseband or near baseband signal; 
 an RF transmitter section coupled to convert an outbound baseband or near baseband signal into an outbound RF signal; 
 a balancing circuit; and 
 a multiple node isolation and coupling circuit comprising a transformer balun having a first winding, a second winding, and a third winding, wherein: the second and third windings are serially coupled, wherein the antenna is coupled to a node of the first winding, the RF receiver section is coupled to a first node of the second winding, the RF transmitter section is coupled to a second node of the third winding, and the balancing circuit is coupled to a series connection of the second and third windings and a plurality of capacitors coupled to the first, second, and third windings, 
 wherein the multiple node isolation and coupling circuit provides the inbound RF signal from the antenna to the RF receiver section and provides the outbound RF signal from the RF transmitter section to the antenna, wherein, by providing an isolating signal to the balancing circuit, the multiple node isolation and coupling circuit substantially isolates the outbound RF signal from the inbound RF signal. 
 
     
     
       11. The IC of  claim 10 , wherein the RF receiver section and the RF transmitter section have substantially equal impedances within a frequency range and frequencies of the inbound and outbound RF signals are within the frequency range such that the transformer balun is a symmetrical transformer balun. 
     
     
       12. The IC of  claim 10 , wherein, within a frequency range, impedance of the RF receiver section does not substantially equal impedance of the RF transmitter section and wherein frequencies of the inbound and outbound RF signals are within the frequency range such that the transformer balun is an asymmetrical transformer balun. 
     
     
       13. The IC of  claim 10 , wherein the multiple node isolation and coupling circuit comprises:
 an autotransformer having a first winding and a second winding coupled in series, wherein a first node of the first winding is coupled to the RF transmitter section and to a first node of the balancing circuit, a second node of the second winding is coupled to the RF receiver section and to a second node of the balancing circuit, a series connection of a second node of the first winding to a first node of the second winding is coupled to the antenna; and 
 a plurality of capacitors coupled to the first and second windings. 
 
     
     
       14. The IC of  claim 10 , wherein the balancing circuit comprises:
 an adjustable impedance network to provide a desired impedance of the balancing circuit with respect to impedances of the RF receiver section and the RF transmitter section. 
 
     
     
       15. The IC of  claim 14 , wherein the balancing circuit further comprises:
 an adjustable capacitor network coupled to the adjustable impedance network, wherein the adjustable capacitor network is adjusted to change an isolation frequency center of the multiple node isolation and coupling circuit. 
 
     
     
       16. The IC of  claim 10 , wherein RF transmitter and RF receiver section are operable to support cellular communications. 
     
     
       17. An integrated circuit (IC) comprises:
 an RF receiver section coupled to convert an inbound RF signal into an inbound baseband or near baseband signal; 
 an RF transmitter section coupled to convert an outbound baseband or near baseband signal into an outbound RF signal; and 
 an isolation circuit coupled to the RF receiver section and the RF transmitter section, wherein the isolation circuit provides a path comprising an adjustable capacitor network coupled to the adjustable impedance network, wherein the adjustable capacitor network is adjusted to change an isolation frequency center of the isolation circuit that carries a substantially equal but opposite current of the outbound RF signal such that, at the RF receiver section, the substantially equal but opposite current of the outbound RF signal substantially cancels current of the outbound RF signal. 
 
     
     
       18. The IC of  claim 17 , wherein the path comprises:
 an adjustable impedance network to provide a desired impedance of the balancing circuit with respect to impedances of the RF receiver section and the RF transmitter section. 
 
     
     
       19. The IC of  claim 17 , wherein the isolation circuit comprises:
 a transformer coupled to the RF receiver section, the RF transmitter section, and an antenna interface. 
 
     
     
       20. The IC of  claim 17 , wherein RF transmitter and RF receiver section are operable to support cellular communications.